In conventional single clutch synchromesh transmission systems for vehicles it is necessary to disengage the transmission from the power source, such as an engine or motor, by operating the clutch before the current gear is deselected and the new gear is engaged. If the power is not disengaged when attempting to engage a new gear the synchromesh is unable to engage the new gear wheel or has to be forced into engagement with the risk of damaging the transmission and creating torque spikes in the transmission. This is because in most cases the speed of the engine is not matched to the speed of the new gear. For motor vehicles such as cars having conventional gearboxes and powered by an engine, the selection of a new gear ratio typically takes between 0.5 and 1 second to complete. So, for example, when a higher gear is selected the time delay allows the engine to reduce its speed [due to its own inertia] to more closely match the speed of the new gear before the clutch re-connects the engine and the transmission, thereby reducing the possibility of torque spikes occurring when the power is reapplied.
In transmission systems where the selection of a new gear ratio takes place almost instantaneously without substantial power interruption, such as the transmission described in PCT/GB2004/001976, large torque spikes can be generated when the new gear is engaged under certain shift conditions. These torque spikes cause shock waves to propagate through the transmission that can be heard and felt by the occupants of the vehicle. The shockwaves can produce a jerky ride for the car occupants and can lead to wear of transmission components and the possibility of components failing. Nevertheless it is desirable to use such a transmission in vehicles since it is more efficient thereby requiring less fuel to operate, produces lower emissions and increases the performance of the car since the application of power is substantially uninterrupted.
For a control system to operate successfully it is important for it to incorporate a means of sensing operational conditions within the transmission. For example, it is often useful to measure or calculate the magnitude and the direction of torque within the transmission to operate control devices that can regulate the torque in the transmission. One approach for measuring torque is to mount a torque sensor on a transmission output shaft for measuring the amount of twist occurring between two known points on the shaft. Torque sensors are very expensive and therefore rarely used in practice. Another drawback is that since the sensor is mounted on the shaft signals must be sent from the sensor to a processing unit via a wireless transmission system or otherwise contact brushes must be mounted about the shaft. There are difficulties in setting up torque sensors using contact brushes and the brushes wear with use and therefore may lead to inaccurate readings or failure of the sensor.